In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad, so that the substrate is polished.
The polishing apparatus for performing the above CMP process includes a polishing table having a polishing pad, and a substrate holding device, which is referred to as a carrier or a top ring, for holding a substrate such as a semiconductor wafer. By using such a polishing apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the substrate holding device, thereby polishing an insulating film or a metal film on the substrate.
After one or more substrates have been polished, abrasive particles or ground-off particles of the substrate are attached to the surface of the polishing pad, and surface configuration or surface condition of the polishing pad is changed, resulting in deterioration in polishing performance. Therefore, as the substrates are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, dressing (conditioning) of the polishing pad is performed to regenerate the surface configuration or surface condition of the polishing pad which has deteriorated.
According to CMP, generally, a combination of consumable members (a pad and a dresser) and pad dressing conditions for achieving a desired CMP performance are applied. However, the consumable members are subject to individual differences and aging variation, and it is necessary to apply optimum dressing conditions in each dressing in order to achieve a stable desired CMP performance. Further, the CMP apparatus is not equipped with a device for measuring pad surface properties such as surface roughness. As a method of measuring surface properties of the polishing pad of CMP, there has been proposed a technology disclosed in Japanese Laid-open patent publication No. 9-119822. According to the proposed method, a liquid that exists at all times on the surface of the pad is removed by gas jet in order to measure the surface properties of the pad.
According to conventional methods, dressing conditions for achieving a stable CMP performance are applied on experiential grounds because information about surface properties of pads has not been obtained. Variations due to individual differences and aging variation of consumable members are tolerated at present.
Further, according to the method disclosed in Japanese Laid-open patent publication No. 9-119822, although it is considered that surface properties of the pad can be obtained, surface properties of the pad cannot be obtained in a wet state of the pad which is prevalent in actual polishing because a liquid film that exists at all times on the pad is removed by gas jet.
On the other hand, if an attempt is made to measure surface properties of the pad by using light in a state where a liquid film exists on the pad surface, then it is problematic that correct information about the pad surface cannot be obtained because the light is reflected and scattered by the interface of the liquid film. Specifically, light emitted from a light emitter travels through the atmosphere, and is then reflected and scattered into the atmosphere by the interface between the air and the liquid film. Only the light that has entered the liquid film from the interface is applied to the surface of the polishing pad. Scattered light that is reflected and scattered by the surface of the polishing pad travels through the liquid film, and is then reflected and scattered into the liquid film by the interface between the liquid film and the air. Only the scattered light that has entered the atmosphere from the interface reaches a light receiver. Consequently, it is problematic that correct information about the pad surface cannot be obtained from the light that has reached the light receiver.